318 MR. S. C. SARKAR ON THE BUCCAL GLANDS 



Conclusions. 



Taking^ a general view of this series, it is interesting to endea- 

 vour to explain the factors which have brought about the gradual 

 change and complicated modifications leading us to the most 

 highly-developed snakes. 



Our hypothetical ancestor of the Aglypha would in all proba- 

 bility be one in which the teeth were equal and peg-like, while 

 the superior labial gland showed no differentiation. The secretion 

 was used more or less for digestive purposes, like the saliva of 

 other animals. The next step in evolution was brought about by 

 the necessity of having a stronger secretion which would have the 

 action of disintegrating the prey more quickly within the mouth. 

 A portion of the gland in the region of the maxilla was differ- 

 entiated to perform this function. The tooth nearest to the 

 opening of the duct of this gland became a little different from 

 the others by acquiring a cutting-edge, and the duct of this 

 portion moved nearer to it. By this arrangement it became 

 possible for the snake to make a deeper and larger scratch and to 

 pour poison on the wound, as in the case of Bendrophis. How- 

 ever, by this method the poison from the now differentiated 

 poison gland is inevitably mixed, and therefore diluted with the 

 general saliva in the mouth. In order to avoid this dilution, the 

 tooth nearest to the opening of the poison gland became bigger 

 and separated from the rest by being enclosed in a special sac. 

 The sac is kept filled with poison, so that the tooth is always 

 immersed in it {Lycodon and Tropidonotus). This ari^ange- 

 ment acted as a sure means of making a deeper wound, which 

 may be compared to poisoning the prey by probing the body 

 with a lancet besmeared with poison. This is undoubtedly 

 a slow process, as a sufficient quantity of poison could not be 

 injected. 



The next step is a great improvement in the tooth — a groove 

 appeared which became almost a canal, as we have seen in 

 Chrysopelea and Dryophis. At the same time, the gland became 

 a distinct organ (text-fig. 21) from the general glandular mass of 

 the superior labial gland, and the duct moved upward to open 

 finally at the base of the tooth. Evidently this is a great advance, 

 for by this means pure unmixed poison can be injected into the 

 deeper tissue. We may compare this with the modern method 

 of injection by a hypodermic or intermuscular syringe, which 

 acted almost instantaneously. This seems to be the origin of the 

 opisthoglyphous snakes. 



But even this method has its defects in some ways. The 

 grooved tooth being sitviated far behind, the prey has to be taken 

 well into the mouth before the operation can be performed. 

 Besides, this tooth cannot be utilised as an organ of offence and 

 defence. Dryophis, in a primitive manner, has overcome this 

 difficulty by developing an extra solid tooth in the anterior end 



